For the purpose of reducing manufacturing cost or weight of liquid containers, paper containers, such as a gable top type paper container and the like, have been conventionally used. In this connection, there has been proposed such a paper container equipped with a pouring plug made of a synthetic resin by which liquid is easily poured from the paper container and which comprises a pourer involving outer screws attached to the pouring port of a liquid container (paper container), an inner plug arranged inside said pourer in an up and down transferable manner, and a cap attached threadedly to said pourer. Said pouring plug has such a construction that said inner plug is forced to break down the film covering the pouring port in case of open the same thereby to opening the plug. Whilst, in case of storing the paper container, said cap has been arranged such that it is fitted into the pourer (see, for example, Japanese Utility Publication No. 37828/1988 official gazette). However, in such type of the pouring plug as described above, it is required to intensely force the inner plug into the plug assembly, by means of fingers, to break down the film as mentioned above, so that there were such problems that the pouring port was difficult to be broken down and that it was not hygienic because the fingers touch the pourer at the time of opening the pouring port.
Furthermore, Japanese Utility Model Publication No. 4558/1987 discloses such construction of a pouring plug that an inner plug which is higher than the pourer is placed inside said pourer, a cap is threadedly attached so as to cover the inner plug projecting from said pourer, and in case of opening a pouring port, said inner plug is depressed while allowing the cap to rotatively lower, thereby breaking down the film. In this pouring plug, however, the cap is located at a high position, a projecting dimension of the whole pouring plug from the liquid container is remarkable, so that the pouring plug itself or a site for attaching the pouring plug in the liquid container is easily damaged because of contact of the pouring plug with something in case of handling such as a conveyance for the liquid container. Moreover, it is required to once rotatively lower the cap in case of breaking down the film, so that opening operation for the pouring port has been troublesome.
On one hand, as described in Japanese Utility Model Publication No. 12335/1986 and Utility Model Laid-open No. 62027/1985, there have been proposed a pouring plug having such construction that an inner plug is screwed with its pourer, and when the cap is rotated, said inner plug descends rotatively to break down a film; and another pouring plug having such construction that a screw rod member threadedly engaged with its inner plug is disposed to a cap, and in case of rotative elevation of the cap, the inner plug is lowered by means of the rotation of said screw rod member thereby breaking down the film. In the construction of the pouring plug disclosed in Utility Model No. 12335/1986, however, it is required that the cap is allowed to rotate in a certain direction in case of opening its pouring port thereby to break down a film, and thereafter said cap is rotated in the reverse direction. In addition, the inner plug must be removed from the pourer so as to be capable of pouring out the contents from the liquid container so that operations for opening the pouring port and pouring out the contents become troublesome. Besides, it was necessary for such complicated operation, that the inner plug was attached to the pourer while rotating said inner plug in case of mounting the pouring plug. On the other hand, the construction of the pouring plug described in Utility Model Laid-open No. 62027/1985 has involved also such disadvantage that an inner plug must have been previously engaged threadedly with a screw rod member disposed on the cap so that operation for attaching the pouring plug becomes complicated. Besides, since a screw portion for engaging threadedly with said screw rod member has been provided at the central portion of the inner plug, a large flowing section cannot be constructed at the central portion of the inner plug, and as a result there was an obstacle to pouring out the contents from the liquid container.
Accordingly, the present invention has been made for the purpose of solving the conventional disadvantages as described above, and an object of which is to provide a pouring plug which can break down a film by means of an easy operation. In addition, it is another object of the present invention to provide a pouring plug having a simple construction and the attachment thereof can easily be effected with respect to a liquid container.